1. Field of the Invention
The present invention relates to a communication apparatus capable of connecting an information processing apparatus.
2. Description of the Related Art
Conventionally, in order to make a radio data communication of data transmitted from an information apparatus via a radio apparatus, the information apparatus and radio apparatus are connected via a wired connection such as RS-232-C, or the like. The radio apparatus encapsulates incoming data from the information apparatus in a radio frame in the radio apparatus, and sends that frame to a partner radio apparatus. Upon receiving the frame, the partner radio apparatus strips off the radio frame wrapping, and sends the data to an information apparatus connected to itself.
In such case, the wired section between the information apparatus and radio apparatus, and the wireless section between the radio apparatuses often use different data transfer rates and data transmission schemes. For example, when the RS-232-C is used in the wired section, the data transfer rate approximately ranges from 9.6 kbps to 115.2 kbps. On the other hand, in the wireless section, although various data transfer rates are available depending on the frequencies and modulation schemes used, when a specific small power radio wave is used, the data transfer rate approximately ranges from 1,200 bps to 4,800 bps. On the other hand, when a spread spectrum communication system such as a radio LAN or the like is used, the data transfer rate approximately ranges from 1 Mbps to 2 Mbps.
Also, as the data transmission scheme the RS-232-C as the wired connection uses start-stop transmission for sequentially transmitting generated transmission data in units of bytes, while the wireless connection uses a scheme of transmitting a packet obtained by packetizing several bytes so as to effectively use a radio wave.
When the wired and wireless sections have different data transfer rates and data transmission schemes, the interval between data transmitted from the information apparatus to the radio apparatus on the transmitting side has changed via the wired and wireless sections on the transmitting side, and the interval of data transmitted to the receiving information apparatus becomes different from that upon transmission in the transmitting information apparatus.
FIG. 1 is a schematic block diagram showing such radio data communication system. FIG. 9 is a timing chart showing the timings of transmission data in the conventional radio data communication system. The aforementioned prior art will be explained below with reference to FIGS. 1 and 9.
Referring to FIG. 1, an information apparatus 101 and radio apparatus 102 are transmitting apparatuses, and are connected via a wired connection. On the other hand, a radio apparatus 103 and information apparatus 104 are receiving apparatuses, and are similarly connected via a wired connection. The radio apparatuses 102 and 103 are connected via a wireless connection.
FIG. 9 shows changes in interval between adjacent data 1 to 3 transmitted by the information apparatus 101 until they are received by the information apparatus 104. Between the information apparatus 101 and radio apparatus 102, the interval between data 1 and 2 is represented by t1, and that between data 2 and 3 by t2. That is, t1 and t2 in this case indicate the data transmission intervals of the information apparatus 101.
When data 1 to 3 are input to the radio apparatus 102, they are encapsulated in radio frames. In this case, data are segmented or combined depending on the data length available in the radio frame. Assume that one data is transmitted using one radio frame.
In the wireless section between the radio apparatuses 102 and 103, data 1 to 3 are transmitted so that the interval between data 1 and 2 changes to T1 and that between data 2 and 3 to T2 as a result of the data processing of the radio apparatus 102. The transmitted data are received by the radio apparatus 103. T1 and T2 are determined by the processing time required for a radio frame encapsulation process and radio frame transmission in the radio apparatus 102, but are roughly constant intervals.
Data 1 to 3 received by the radio apparatus 103 are stripped off the radio frame wrappings, and are transmitted to the information apparatus 104. In this case, the transmission intervals between adjacent data are the same as those of data received by the radio apparatus 103, i.e., the interval between data 1 and 2 is T1, and that between data 2 and 3 is T2.
As described above, in the prior art, the transmission interval of data transmitted by the transmitting information apparatus 101 does not match the reception interval of data received by the receiving information apparatus 104. The data interval is determined by the data transfer rate and processing speed in the wireless section between the radio apparatuses 102 and 103, and the transmission interval of data intended by the transmitting information apparatus 101 changes by the time the data are received by the information apparatus 104.
When the data reception interval has changed between the transmitting and receiving information apparatuses 101 and 104, if moving images or quasi-still images displayed at given intervals on the information apparatus 101 are simultaneously transferred to and displayed on the information apparatus 104, changes in frame in the information apparatus 101 cannot be synchronized with those in the information apparatus 104, resulting in unnatural image display.
It is an object of the present invention to provide a radio data communication system and scheme, which can suppress variations of such data time intervals, and can synchronize the data time intervals between the transmitting and receiving sides even when data are transmitted using a wireless section.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.